The invention relates generally to installing thermoplastic replacement pipe, and more particularly to a method and apparatus for rounding replacement pipe that is installed in an existing conduit in a reduced condition and is expanded to the interior dimensions of the existing pipeline.
The repair and rehabilitation of underground pipelines, such as sewerlines and other conduits is an important and widespread task. The NuPipe.RTM. method for effecting such repair is described in U.S. Pat. Nos. 4,867,921 and 5,034,180, assigned to NuPipe, Inc. of Memphis, Tennessee. The contents of these patents which describe the installation of a replacement pipe formed of rigid thermoplastic material within an existing conduit are incorporated herein by reference. In the NuPipe.RTM. process a replacement thermoplastic pipe in a flattened and folded form is stored on a reel. The pipe is heated at the installation site in order to make it flexible enough to be inserted into an existing manhole, pulled into place and then sequentially expanded to a round condition by internal pressure. This creates a tight fit against the original conduit being repaired. In this position the now rounded pipe is cooled to a rigid state while internal pressure is maintained, creating a permanent replacement pipe with lateral connections cut from within.
The NuPipe.RTM. process of repair is advantageous for underground conduits because it requires little or no excavation and removal of the existing pipeline. It produces a pipe with the physical properties of a thermoplastic pipe of the same thickness and diameter. In addition, the NuPipe.RTM. process does not materially reduce the diameter of the pre-existing conduit, eliminates annular space between the replacement pipe and the conduit, and eliminates the need for grouting. Thus, repair and rehabilitation can be accomplished in a convenient and effective manner with minimal disruption of traffic and commercial activity.
FIG. 1 illustrates the NuPipe.RTM. process for an existing underground conduit 10 which extends between a pair of manholes 12 and 13 that provide access to conduit 10 from ground level 14. A length of rigid thermoplastic replacement pipe 22 in a flattened and folded (or in another reduced shape) reduced condition is brought to the installation site on a spool 24 in a trailer or a truck 26. Pipe 22 is heated to render it flexible and is pulled into existing conduit 10 by a pull cable 30 connected to a cable winch 28 adjacent to manhole 13. The reduced condition of thermoplastic replacement pipe 22 is a preferred configuration as described in connection with the NuPipe.RTM. process and is illustrated in FIG. 2 within conduit 10. Thermoplastic pipe 22 is shown after expansion and rounding in FIGS. 3 and 6. Pipe 22 is typically heated and rendered flexible for insertion into the conduit by heating a spool 24 of folded pipe 22 within a housing 25 on vehicle 26 at the installation site.
After inserting pipe 22 in conduit 10, it can be expanded by several conventional methods. A first method involves installing a pair of plugs at opposite ends of the pipe and inflating the pipe with fluid, such as pressurized steam, hot water or hot air. Another method involves pulling a heated mandrel through the pipe.
Another embodiment of the NuPipe.RTM. process involves installation with the use of a heat containment tube 16 as shown in FIG. 4. Heat containment tube 16 is a thin, flexible, tubular membrane installed between conduit 10 and pipe 22. Tube 16 can be manufactured from any material which is strong, pliable, air and water tight, and capable of withstanding live steam at high temperatures of up to 250.degree. F. and substantial internal pressures. A suitable membrane for this purpose has been found to be a nylon reinforced polyethylene, 0.006 inches thick, although other suitable membrane material would also suffice, ranging in thickness from about 0.003 to 0.020 inches.
Installation using heat containment tube 16 is described in detail in U.S. Pat. No. 5,034,180. First, heat containment tube 16 can be pulled through a section of the existing conduit from manhole 12 to manhole 13 with some extra length of the tubing extending from each end of the section of conduit to be rebuilt. The diameter of tube 16 is preferably at least as great or greater than the inside diameter of existing conduit 10.
With tube 16 extending the full length of conduit 10, an end of tube 16 is temporarily connected to an air blower 18 and air is blown through tube 16 to expand it. With tube 16 expanded, heated and flexible folded replacement pipe 22 is pulled through heat containment tube 16 using winch 28 and cable 30.
With folded replacement pipe 22 in place within heat containment tube 16, a hot fluid, preferably steam, is introduced into an end of tube 16 while the opposite end of tube 16 is closed or restricted. If fluids need to be expelled or prevented from entering the existing conduit, steam or a combination of steam and air are injected into heat containment tube 16 in sufficient volume to maintain enough pressure within the tube to expel or prevent the entrance of such fluids.
If steam is used, a steam hose connected to a source of steam can be connected to an end of tube 16 and the other end can be tied shut. The steam is forced down through the length of tube 16 on the outside of folded pipe 22 and then back in the opposite direction through tube 16 but within folded pipe 22. Alternatively, the steam can be introduced initially into an end of folded pipe 22 and then passed back in the opposition direction on the outside of pipe 22 within tube 16. Another alternative is to restrict tube 16 at an end and allow the hot fluid inside both tube 16 and pipe 22. Each routing of the steam provides quick and effective full-length internal and external heating of pipe 22.
With thermoplastic replacement pipe 22 in a heated, flexible condition within tube 16, pipe 22 is rounded and expanded. If the heat containment tube 16 is supplied with a coating of compressible gasket material, a continuous seal is formed between the interior wall of existing conduit 10 and the exterior wall of the rounded and expanded pipe 22.
U.S. Pat. No. 5,034,180 describes the use of a heat containment tube and a expansion device. The expansion device is propelled through the collapsed pipe by forcing steam behind the expansion device and permitting some steam to flow past the expansion device so that the entire thermoplastic pipe remains heated during expansion. Other methods can involve pulling a heated mandrel through the installed pipe. The pipe is then permitted to cool under internal fluid pressure to prevent it from collapsing.
These known methods for expanding and rounding the thermoplastic replacement pipe all utilize a heated fluid to provide internal pressure and thus have drawbacks. A considerable amount of steam is required and this increases energy costs and risk of injury. The use of hot fluid also leads to expansion, compression and thermal shrinkage induced tensile stresses built up in the expanded pipe, which can result in the formation of cracks. Accordingly, it is desirable to provide a new method and apparatus for expanding a thermoplastic replacement pipe within an existing conduit which overcomes these shortcomings.